ShopGame/Assets/Scripts/ItemPickup.cs

using UnityEngine;
using UnityEngine.InputSystem;

public class ItemPickup : MonoBehaviour
{
    [Header("Layer Settings")]
    public LayerMask pickupLayer;
    [Header("Input Settings")]
    public InputActionAsset inputActionAsset;

    [Header("Pickup Settings")]
    public float pickupSpeed = 10f; // How fast it snaps to your hand
    public float holdDistance = 3f;  // Default distance

    private InputAction pickUpAction;
    private Camera mainCamera;
    
    // We store the Rigidbody instead of the GameObject
    private Rigidbody currentPickedRB = null; 

    void Awake()
    {
        mainCamera = Camera.main;
    }

    private void OnEnable()
    {
        if (inputActionAsset != null)
        {
            pickUpAction = inputActionAsset.FindAction("PickUp");
            if (pickUpAction != null)
            {
                pickUpAction.Enable();
                pickUpAction.started += OnPickUpStarted;
                pickUpAction.canceled += OnPickUpCanceled;
            }
        }
    }

    private void OnDisable()
    {
        if (pickUpAction != null)
        {
            pickUpAction.started -= OnPickUpStarted;
            pickUpAction.canceled -= OnPickUpCanceled;
            pickUpAction.Disable();
        }
    }

    private void OnPickUpStarted(InputAction.CallbackContext context)
    {
        // 1. Raycast to find object
        Vector2 mousePos = Mouse.current.position.ReadValue();
        Ray ray = mainCamera.ScreenPointToRay(mousePos);
        RaycastHit hit;

        if (Physics.Raycast(ray, out hit))
        {
            // Check if it has a Rigidbody and match layer
            if (hit.collider.TryGetComponent(out Rigidbody rb) && 
                ((1 << hit.collider.gameObject.layer) & pickupLayer) != 0)
            {
                currentPickedRB = rb;
                
                // --- CRITICAL FIX START ---
                // If we pick it off a Shelf, it is frozen (Kinematic). 
                // We must unfreeze it immediately so we can apply velocity.
                currentPickedRB.isKinematic = false; 
                // --- CRITICAL FIX END ---

                // 2. Setup Physics for "Holding"
                currentPickedRB.useGravity = false; 
                
                // Add damping so it doesn't drift around like it's on ice
                currentPickedRB.linearDamping = 10; 
                currentPickedRB.angularDamping = 5;

                // Optional: Calculate distance to keep it where we clicked
                holdDistance = hit.distance;

                // Notify RayCastSystem
                RayCastSystem rayCastSystem = GetComponent<RayCastSystem>();
                if (rayCastSystem != null)
                {
                    rayCastSystem.SetCurrentPickedRB(rb);
                }
            }
        }
    }

    private void OnPickUpCanceled(InputAction.CallbackContext context)
    {
        if (currentPickedRB != null)
        {
            // 3. Reset Physics properties
            currentPickedRB.useGravity = true;
            currentPickedRB.linearDamping = 0; // Reset to default (usually 0)
            currentPickedRB.angularDamping = 0.05f;

            currentPickedRB = null;
            // Notify RayCastSystem that an object is no longer picked up
            RayCastSystem rayCastSystem = GetComponent<RayCastSystem>();
            if (rayCastSystem != null)
            {
                rayCastSystem.SetCurrentPickedRB(null);
            }
        }
    }

    // Physics movement must be in FixedUpdate
    private void FixedUpdate()
    {
        if (currentPickedRB != null)
        {
            MoveObjectPhysics();
        }
    }

    private void MoveObjectPhysics()
    {
        Vector2 mousePos = Mouse.current.position.ReadValue();
        Ray ray = mainCamera.ScreenPointToRay(mousePos);

        // Where we want the object to be
        Vector3 targetPosition = ray.GetPoint(holdDistance);

        // Calculate direction vector: Target - Current
        Vector3 direction = targetPosition - currentPickedRB.position;

        // Apply Velocity
        // We multiply by pickupSpeed to make it responsive
        // The physics engine handles the rest (Mass 1 vs Mass 100 collisions)
        currentPickedRB.linearVelocity = direction * pickupSpeed;

        // Note: In Unity versions older than 2023.3, use 'velocity' instead of 'linearVelocity'
        // currentPickedRB.velocity = direction * pickupSpeed;
    }
}